The invention generally relates to processes and catalyst precursor compositions useful for the hydrocyanation of monoolefins. In particular, the invention relates to the hydrocyanation of monoolefins using catalyst precursor compositions comprising zero-valent nickel and unsymmetrical bidentate phosphite ligands.
Hydrocyanation catalyst systems, particularly pertaining to the hydrocyanation of olefins, are known in the art. For example, systems useful for the hydrocyanation of butadiene to form pentenenitrile (PN) and in the subsequent hydrocyanation of pentenenitrile (PN) to form adiponitrile (ADN), are known in the commercially important nylon synthesis field.
The hydrocyanation of olefins using transition metal complexes with monodentate phosphite ligand is documented in the prior art. See for example; U.S. Pat. Nos. 3,496,215, 3,631,191, 3,655,723 and 3,766,237, and Tolman, C. A.; McKinney, R. J.; Seidel, W. C.; Druliner, J. D.; and Stevens, W. R.; Advances in Catalysis, 33, 1, 1985.
The hydrocyanation of activated olefins such as with conjugated olefins (e.g., butadiene and styrene) and strained olefins (e.g., norbornene) proceeds without the use of a Lewis acid promoter, while hydrocyanation of unactivated olefins such as 1-octene and 3-pentene-nitrile requires the use of a Lewis acid promoter. Teachings regarding the use of a promoter in the hydrocyanation reaction appear, for example, in U.S. Pat. No. 3,496,217. This patent discloses an improvement in hydrocyanation using a promoter selected from a large number of metal cation compounds with a variety of anions as catalyst promoters.
U.S. Pat. No. 3,496,218 discloses a nickel hydrocyanation catalyst promoted with various boron-containing compounds, including triphenylboron and alkali metal borohydrides. U.S. Pat. No. 4,774,353 discloses a process for the preparation of dinitriles, including ADN, from unsaturated nitriles, including PN, in the presence of a zero-valent nickel catalyst and a triorganotin catalyst promoter. U.S. Pat. No. 4,874,884 discloses a process for producing ADN by the zero-valent nickel catalyzed hydrocyanation of pentenenitriles in the presence of a synergistic combination of promoters selected in accordance with the reaction kinetics of the ADN synthesis.
Bidentate phosphite ligands similar to those used in the present invention for the hydrocyanation of monoolefins have been shown to be useful ligands in the hydrocyanation of activated olefins. See, for example: Baker, M. J., and Pringle, P. G.; J. Chem. Soc., Chem. Commun., 1292, 1991; Baker, M. J.; Harrison, K. N.; Orpen, A. G.; Pringle, P. G.; and Shaw, G.; J. Chem. Soc.; Chem. Commun., 803, 1991, Union Carbide, WO 93,03839. Also, similar ligands have been disclosed with rhodium in the hydroformylation of functionalized olefins; Cuny et al., J. Am. Chem. Soc. 1993, 115, 2066.
The present invention provides novel processes and catalyst precursor compositions which are rapid, selective, efficient and stable in the hydrocyanation of monoolefins. Other objects and advantages of the present invention will become apparent to those skilled in the art upon reference to the detailed description which hereinafter follows.
The present invention provides a process for hydro-cyanation, comprising reacting a nonconjugated acyclic aliphatic monoolefin or a monoolefin conjugated to an ester group; e.g., methyl pent-2-eneoate, with a source of HCN in the presence of a catalyst precursor composition comprising zero-valent nickel and a bidentate phosphite ligand of Formula I, 
wherein
each R1 is independently a secondary or tertiary substituted hydrocarbyl of 3 to 12 carbon atoms;
each R2 is independently, H, X wherein X is Cl, F or Br, a C1 to C12 alkyl, or OR3 wherein R3 is C1 to C12 alkyl;
to produce a terminal organonitrile. Preferably, the reaction is carried out in the presence of a Lewis acid promoter.
The present invention also provides a process for hydrocyanation comprising reacting a nonconjugated acyclic aliphatic monoolefin or a monoolefin conjugated to an ester group; e.g., methyl pent-2-eneoate, with a source of HCN in the presence of a catalyst precursor composition comprising zero-valent nickel and a bidentate phosphite ligand selected from the group consisting of Formulas II-VI as set forth below: 
wherein
each R6 is independently a secondary or tertiary substituted hydrocarbyl of 3 to 12 carbon atoms; and
each R7 is independently H, X wherein X is Cl, F or Br, a C1 to C12 alkyl, or OR8 wherein R8 is C1 to C12 alkyl; 
wherein
each R9 is independently a secondary or tertiary substituted hydrocarbyl of 3 to 12 carbon atoms;
each R10 is independently H, X wherein X is Cl, F or Br, a C1 to C12 alkyl, or OR8 wherein R8 is C1 to C12 alkyl; and
each R11 is independently a branched or straight chain alkyl of up to 12 carbon atoms; 
wherein
each R12 is independently a secondary or tertiary substituted hydrocarbyl of 3 to 12 carbon atoms;
each R13 is independently H, X wherein X is Cl, F or Br, a C1 to C12 alkyl, or OR8 wherein R8 is C1 to C12 alkyl; and
each R14 is independently a branched or straight chain alkyl of up to 12 carbon atoms; 
wherein
each R15 is independently a secondary or tertiary substituted hydrocarbyl of 3 to 12 carbon atoms; and
each R16 is independently H, X wherein X is Cl, F or Br, a C1 to C12 alkyl, or OR8 wherein R8 is C1 to C12 alkyl;
and 
wherein
each R17 is independently a secondary or tertiary substituted hydrocarbyl of 3 to 12 carbon atoms; and
each R18 is independently H, X wherein X is Cl, F or Br, a C1 to C12 alkyl, or OR8 wherein R8 is C1 to C12 alkyl;
to produce a terminal organonitrile. Preferably, the reaction is carried out in the presence of a Lewis acid promoter.
The monoolefins of the above-identified processes are described by Formulas VII or IX, and the corresponding terminal organonitrile compounds produced are described by Formulas VIII or X, respectively. 
wherein
R19 is H, CN, CO2R20, or perfluoroalkyl;
y is 0 to 12;
x is 0 to 12 when R19 is H, CO2R20 or perfluoroalkyl;
x is 1 to 12 when R19 is CN; and
R20 is alkyl; or 
wherein
R19 is H, CN, CO2R20, or perfluoroalkyl;
x is 0 to 12 when R19 is H, CO2R20 or perfluoroalkyl;
x is 1 to 12 when R19 is CN; and
R20 is alkyl.
The present invention further provides a catalyst precursor composition comprising zero-valent nickel and an unsymmetrical bidentate phosphite ligand of Formula I, 
wherein
each R1 is independently a secondary or tertiary substituted hydrocarbon of 3 to 12 carbon atoms; and
each R2 is independently H, X wherein X is Cl, F or Br, a C1 to C12 alkyl, or OR3 wherein R3 is C1 to C12 alkyl.
The present invention further provides a catalyst precursor composition comprising zero-valent nickel and an unsymmetrical bidentate phosphite ligand selected from the group consisting of Formulas II-VI as set forth below: 
wherein
each R6 is independently a secondary or tertiary substituted hydrocarbyl of 3 to 12 carbon atoms; and
each R7 is independently H, X wherein X is Cl, F or Br, a C1 to C12 alkyl, or OR8 wherein R8 is C1 to C12 alkyl; 
wherein
each R9 is independently a secondary or tertiary substituted hydrocarbyl of 3 to 12 carbon atoms;
each R10 is independently H, X wherein X is Cl, F or Br, a C1 to C12 alkyl, or OR8 wherein R8 is C1 to C12 alkyl; and
each R11 is independently a branched or straight chain alkyl of up to 12 carbon atoms; 
wherein
each R12 is independently a secondary or tertiary substituted hydrocarbyl of 3 to 12 carbon atoms;
each R13 is independently H, X wherein X is Cl, F or Br, a C1 to C12 alkyl, or OR8 wherein R8 is C1 to C12 alkyl; and
each R14 is independently a branched or straight chain alkyl of up to 12 carbon atoms; 
wherein
each R15 is independently a secondary or tertiary substituted hydrocarbyl of 3 to 12 carbon atoms; and
each R16 is independently H, X wherein X is Cl, F or Br, a C1 to C12 alkyl, or OR8 wherein R8 is C1 to C12 alkyl;
and 
wherein
each R17 is independently a secondary or tertiary substituted hydrocarbyl of 3 to 12 carbon atoms; and
each R18 is independently H, X wherein X is Cl, F or Br, a C1 to C12 alkyl, or OR8 wherein R8 is C1 to C12 alkyl.
Preferably, the catalyst precursor compositions of Formulas I-VI further comprise a Lewis acid promoter.
The catalyst precursor compositions of the invention are comprised of a bidentate phosphite ligand and zero-valent nickel. The preferred ligand of the invention is described below by Formula I, wherein each R2 is independently H, or a C1 to C12 alkyl, or OR3 wherein R3 is a C1 to C12 alkyl. Alkyl includes straight chain or branched groups. R3 can be primary, secondary or tertiary; examples include methyl, ethyl, isopropyl and t-butyl. Each R2 may be the same or different. In the preferred ligand, all R2 groups are H, except for the two R2 groups meta to the R1 groups. These R2 groups are OR3 wherein R3 is methyl. R1 is a secondary or tertiary substituted hydrocarbyl group containing up to 12 single bond carbon atoms. In the preferred ligand, both R1 groups are tertiary butyl. 
As used herein, the terms xe2x80x9csecondary or tertiary substitutedxe2x80x9d refer to the first carbon of the hydrocarbyl which is attached to the ring. The term xe2x80x9chydrocarbylxe2x80x9d generally refers to a straight chain, branched or aryl carbon structure containing single, double or triple bonds, and substituted accordingly with hydrogen.
Applicants have referred to the catalyst composition of the invention as a xe2x80x9cprecursorxe2x80x9d composition only to indicate that, in all likelihood, during the hydrocyanation reaction the structure of the active catalyst composition may in fact be complexed to an olefin.
The preferred ligands of the invention (i.e., Formula I) may be prepared by a variety of methods known in the art, for example see descriptions in WO 93,03839, U.S. Pat. No. 4,769,498; U.S. Pat. No. 4,688,651, J. Amer. Chem. Soc., 115, 2066, 1993. The reaction of 2,2xe2x80x2-biphenol with phosphorus trichloride gives 1,1xe2x80x2-biphenyl-2,2xe2x80x2-diyl phosphorochloridite. The reaction of this chloroidite with 2,2xe2x80x2-dihydroxy-3,3xe2x80x2-di-t-butyl-5,5xe2x80x2-dialkoxy-1,1xe2x80x2-biphenyl in the presence of triethylamine gives the preferred bidentate phosphite ligand wherein R1 is t-butyl.
Other bidentate phosphite ligands of the invention are described above by Formulas II-VI. While these ligands may not be as presently preferred as Formula I, they nevertheless are considered useful ligands of the present invention. These ligands may be prepared by a variety of methods known in the art; for example, see U.S. Pat. No. 5,202,297, the contents of which are incorporated herein. According to U.S. Pat. No. 5,202,297, phosphorus trichloride is reacted with a diol to form a monochlorophosphite which is reacted with a diol to form a hydroxyl-substituted diorganophosphite. This diorganophosphite intermediate is reacted with another monochlorophosphite to give the unsymmetrical bidentate phosphite ligands of Formulas II-VI.
The zero-valent nickel can be prepared or generated according to techniques well known in the art (U.S. Pat. Nos. 3,496,217; 3,631,191; 3,846,461; 3,847,959; and 3,903,120 which are incorporated by reference). Zero-valent nickel compounds that contain ligands which can be displaced by the organophosphorus ligand are a preferred source of zero-valent nickel. Two such preferred zero-valent nickel compounds are Ni(COD)2 (COD is 1,5-cyclooctadiene) and Ni(P(O-o-C6H4CH3)3)2(C2H4), both of which are known in the art. Alternatively, divalent nickel compounds may be combined with a reducing agent, and are then able to serve as suitable sources of zero-valent nickel in the reaction. Suitable divalent nickel compounds include compounds of the formula NiY2 where Y is halide, carboxylate, or acetylacetonate. Suitable reducing agents include metal borohydrides, metal aluminum hydrides, metal alkyls, Zn, Fe, Al, Na, or H2. Elemental nickel, preferably nickel powder, when combined with a halogenated cataylst, as described in U.S. Pat. No. 3,903,120, is also a suitable source of zero-valent nickel.
The nonconjugated acyclic aliphatic monoolefin substrates of the invention include unsaturated organic compounds containing from 2 to approximately 30 carbon atoms having at least one nonconjugated aliphatic carbon-carbon double bond. The 3-pentenenitrile and 4-pentenenitrile are especially preferred. As a practical matter, when the nonconjugated acyclic aliphatic monoolefins are used in accordance with this invention, up to about 10% by weight of the monoolefin may be present in the form of a conjugated isomer, which itself may be subject to hydrocyanation. For example, when 3-pentenenitrile is used, as much as 10% by weight thereof may be 2-pentenenitrile. Suitable unsaturated compounds include olefins and olefins substituted with groups which do not attack the catalyst, such as cyano. These unsaturated compounds include monoolefins containing from 2 to 30 carbons such as ethylene, propylene, butene-1, pentene-2, hexene-2, etc., nonconjugated diolefins such as allene, and substituted compounds such as 3-pentenenitrile, 4-pentenenitrile and methyl pent-3-enoate. The monoolefins may also be conjugated to an ester group such as methyl pent-2-enoate.
Two formulas are presented below which together describe these substrates of the invention; Formulas VII and IX. Substrates of Formula VII yield terminal organonitriles of Formula VIII, while Formula IX substrates will yield terminal organonitriles of Formula X.
CH3xe2x80x94(CH2)yxe2x80x94CHxe2x95x90CHxe2x80x94(CH2)xxe2x80x94R19xe2x80x83xe2x80x83VII
wherein
R19 is H, CN, CO2R20, or perfluoroalkyl;
y is 0 to 12;
x is 0 to 12 when R19 is H, CO2R20 or perfluoroalkyl;
x is 1 to 12 when R19 is CN; and
R20 is alkyl;
produces the terminal organonitrile product compound of Formula VIII
NCxe2x80x94(CH2)y+x+3xe2x80x94R19xe2x80x83xe2x80x83VIII
wherein
R19, y and x are as defined above.
CH2xe2x95x90CHxe2x80x94(CH2)xR19xe2x80x83xe2x80x83IX
wherein
R19 is H, CN, CO2R20, or perfluoroalkyl;
x is 0 to 12 when R19 is H, CO2R20 or perfluoroalkyl;
x is 1 to 12 when R19 is CN; and
R20 is alkyl,
produces the terminal organonitrile product compound of Formula X
NCxe2x80x94(CH2)x+2xe2x80x94R19xe2x80x83xe2x80x83X
wherein
R19 and x are as defined above.
Perfluoroalkyl is defined as CzF2z+1 where z is 1 to 12.
Preferred substrates are nonconjugated linear alkenes, nonconjugated linear alkenenitriles, nonconjugated linear alkenoates, linear alk-2-enoates and perfluoroalkyl ethylenes. Most preferred substrates include 3- and 4-pentenenitrile, alkyl 2- and 3- and 4-penteneoates, and CzF2z+1CHxe2x95x90CH2 (where z is 1 to 12).
The preferred products are terminal alkanenitriles, linear alkanedinitriles, linear alkane(nitrile)esters, and 3-(perfluoroalkyl)propionitrile. Most preferred products are adiponitrile, alkyl 5-cyanovalerate, and CzF2z+1CH2CH2CN (where z is 1 to 12).
The present hydrocyanation process may be carried out by charging a reactor with all of the reactants, or preferably the reactor is charged with the catalyst precursor or catalyst components, the unsaturated organic compound, the promoter and the solvent to be used and the hydrogen cyanide added slowly. HCN may be delivered as a liquid or as a vapor to the reaction. Another technique is to charge the reactor with the catalyst, promoter, and the solvent to be used, and feed both the unsaturated compound and the HCN slowly to the reaction mixture. The molar ratio of unsaturated compound to catalyst generally is varied from about 10:1 to 2000:1.
Preferably, the reaction medium is agitated, such as by stirring or shaking. The cyanated product can be recovered by conventional techniques such as by distillation. The reaction may be run either batchwise or in a continuous manner.
The hydrocyanation reaction can be carried out with or without a solvent. The solvent should be liquid at the reaction temperature and pressure and inert towards the unsaturated compound and the catalyst. Generally, such solvents are hydrocarbons such as benzene or xylene, or nitriles such as acetonitrile or benzonitrile. In some cases, the unsaturated compound to be hydrocyanated may serve as the solvent.
The exact temperature which is preferred is dependent to a certain extent on the particular catalyst being used, the particular unsaturated compound being used and the desired rate. Generally, temperatures of from xe2x88x9225 to 200xc2x0 C. can be used, with from 0 to 150xc2x0 C. being preferred.
Atmospheric pressure is satisfactory for carrying out the present invention and hence pressure of from about 0.05 to 10 atmospheres are preferred due to the obvious economic considerations although pressures of from 0.05 to 100 atmospheres can be used if desired.
HCN may be added to the reaction as vapor or liquid, or in a system utilizing a cyanohydrin as carrier. See, for example, U.S. Pat. No. 3,655,723 which is incorporated herein by reference.
Typically, the processes of this invention are carried out in the presence of one or more Lewis acid promoters which affect both the activity and selectivity of the catalyst system. However, it should be understood that the presence of a Lewis acid promoter is not deemed critical to the invention, although it is preferred. The promoter may be an inorganic or organo-metallic compound in which the cation is selected from the group consisting of scandium, titanium, vanadium, chromium, manganese, iron, cobalt, copper, zinc, boron, aluminum, yttrium, zirconium, niobium, molybdenum, cadmium, rhenium and tin. Examples include ZnBr2, ZnI2, ZnCl2, ZnSO4, CuCl2, CuCl, Cu(O3SCF3)2, COCl2, CoI2, FeCl2, FeI2, FeCl3, FeCl2(THF)2, TiCl4(THF)2, TiCl4, TiCl3, ClTi(OiPr)3, MnCl2, ScCl3, AlCl3, (C8H17)AlCl2, (C8H17)2AlCl, (i-C4H9)2AlCl, Ph2AlCl, PhAlCl2, ReCl5, ZrCl4, NbCl5, VCl3, CrCl2, MoCl5, YCl3, CdCl2, LaCl3, Er(O3SCF3)3, Yb(O2CCF3)3, SmCl3, BPh3, TaCl5. Suitable promoters are further described in U.S. Pat. No. 3,496,217; U.S. Pat. No. 3,496,218,; U.S. Pat. No. 4,774,353. These include metal salts (such as ZnCl2, CoI2, and SnCl2), and organometallic compounds (such as RAlCl2, R3SnO3SCF3, and R3B, where R is an alkyl or aryl group).
U.S. Pat. No. 4,874,884 describes how synergistic combinations of promoters may be chosen to increase the catalytic activity of the catalyst system. Preferred promoters are CdCl2, ZnCl2, B(C6H5)3, and (C6H5)3SnX, where X=CF3SO3, CH3C6H5SO3, or (C6H5)3BCN. The amount of promoter to nickel present in the reaction may be in the range of 1:16 to 50:1.